"Materials really are the basis of almost every technology that's out there."

Seth Darling is a scientist at Argonne's Center for Nanoscale Materials. He builds new materials for solar energy, with the aim of creating cheaper and more efficient solar cells.

Question: How did you first get interested in science?

Seth Darling: I can't remember back that far. I've been interested in science as long as I can remember. Yeah, all the way back to elementary school—I was certain I was going to be a scientist at that point.

Chemistry was the plan for many years; all the way up even into college I was planning to do chemistry. And now I do something that uses chemistry, but is really chemistry and physics and materials science and nanoscience and all kinds of stuff all rolled up together.

Q: What do you like about that?

SD: It's fun because you get to work with a very diverse group of scientists. Postdocs who work with me have degrees in electrical engineering and chemistry and material science. So it's fun because you can really look at the interfaces between these different disciplines, which is where most of the interesting stuff is going on. It's also very challenging because there's just no way you can be an expert on all of those simultaneously, and so you always feel a little bit like you're at the edge of your understanding. Which is challenging, but it's also fun—you get to learn lots of new stuff all the time.

Q: What projects are you working on now?

SD: Most of what I'm working on now revolves around solar energy: photovoltaics, specifically. What we're interested in are organic photovoltaics, and photovoltaics that involve organic materials that might also involve inorganic materials—hybrids. We're interested in those because they're significantly lower-cost than current solar energy technologies, but right now the efficiencies are not high enough to be truly commercially relevant. So we're doing the basic science to understand where the efficiency losses are, and how can they be improved. These are basic science questions, but are also very much geared towards the applied side—ultimately pushing commercial industry towards organic photovoltaics. That's where most of our work lies.

Mostly what I do is what I would call "polymer molecular engineering." Right now we're working with people in Argonne's Energy Systems division to develop a new material synthesis technique. It's called sequential infiltration synthesis, which is a mouthful, so we call it SIS. Basically, it's taking polymer films and exposing them to gas-phase molecular precursors for inorganic materials. It's related to atomic layer deposition, but ALD is depositing a coating on top of a material, whereas here we're penetrating those precursors into the polymer film.

Q: What can you do with SIS?

SD: There are lots of things you can do with this. For example, you can use materials like block copolymers, which are polymers made up of two different types of polymers that self-assemble into various nanostructures. And what you can do is use a specific chemistry in your sequential infiltration synthesis that's selective for only one of those polymers. So you'll grow material inside one of those polymer materials but not inside the material around it, for example. What that allows you to do is to take the self-assembled polymeric material, which may not have any real useful functionality in and of itself—it's just sort of insulating polymer—but then you can grow inorganic material, which can have diverse functionality. It can be a semiconductor or magnetic material or metallic material for wires, for example. So you can have self-assembled nanowires or all sorts of different things. You can grow multilayers. You can get three dimensional structures.

Q: And those are all for photovoltaics?

SD: Well, it's not actually; you can do all kinds of things with those. You can do catalytic applications. You can imagine electronics applications. You can imagine filtration applications. All sorts of different things where you need nanostructures, but you also need the functionality of inorganic material, whether it's mechanical functionality or electrical functionality or magnetic functionality. So you can grow lots of different materials using SIS.

Q: What are the steps to coming up with a new process? How does that happen?

SD: Well, you know there's not a recipe to follow to come up with a new idea; that's not really how it happens. The way this one went down was that a postdoc who works with Jeff Elam, Qing Peng, had some experience with polymers and with atomic layer deposition. They contacted me because they knew I worked with block copolymers. And we sat down for lunch one day in the Argonne cafeteria. He said, "What do you think about trying to apply something like atomic layer deposition to block copolymers? I think we might be able to get selectivity."

I said, "That's never gonna work." Because atomic layer deposition, if you're familiar with it, you're just used to thinking of it as a coating on top of materials. You don't picture the materials diffusing in, and that's sort of the whole point, is that they don't diffuse into the materials normally. So I said, "That's never gonna work but I'm gonna give it a shot cause it's easy enough to try, and if it works, it'd be very cool." And it was one of those rare experiments that worked the first time we tried it. Like, perfectly. And we've been running with it ever since, because we just keep coming up with new cool things that we can do.

Q: So it's unusual for experiments to work the first time?

SD: Yeah. That almost never happens. I mean, sometimes you have something fortuitous where it doesn't work the first time but then it works in a different way later; sometimes that's how you end up coming up with a new idea. But this particular breakthrough, Qing had an idea and it went down exactly the way he thought it would—where I was skeptical about it—but it worked perfectly.

Q: What keeps you interested in your work?

SD: Well, solar energy is something I got interested in about eight years ago. I saw a presentation by a CalTech professor whose name is Nate Lewis. He was at a big conference in D.C. on nanoscience. Until that point my research had always been very basic; fundamental physical chemistry, fundamental materials science.

But he gave a very compelling presentation on climate change, and specifically, how solar energy has to be one of the critical approaches to mitigating climate change. And I walked out of the presentation thinking, "I'm a scientist, there must be some way I can make some kind of impact in this area."

It took me a few years to come up with something. But it was the first time in my career when I was really driven, not just out of scientific curiosity but out of—almost a moral imperative. I guess it felt like, here is this societal crisis; and if there's any way that you have a shot at helping with that, you should. And so that's what made me want to get into it, and eventually I figured out some ways to do some work in the area. You're working towards trying to save the world, and what better reason is there to come to work every day than to try to make the world better?

Q: What is the biggest challenge in your field?

SD: Well, for solar energy, basically the challenge is to have large scale utilization of solar energy. That is the challenge. And the way you do that is by lowering the costs of scalable technologies.

But I do think that outside of solar energy, the challenge is basically pushing the limits of what you can do with materials. Materials really are the basis of almost every technology that's out there.

So we're looking at a technique called lithography in one direction. Lithography is the basis for the entire microelectronics industry. Information technology is all based on that kind of stuff. So if you can improve the limits of lithography, you can push the limits of microelectronics, which can therefore push the limits of what computers can do, and so on. And if you start taking these materials and applying them to catalysis, you can look for more effective catalysts, which can dramatically decrease costs for all kinds of different chemical processing. You can use the materials for filtration/separation membranes, which could make water purification more effective. Or make desalination a more efficient process which could help impact growing water resource issues. So you have to pick the direction you're gonna push your materials, and sadly, our group can't do all those simultaneous things.

Q: You wish you could?

SD: Well, yeah. That would be really wonderful. Just get another four or five 24-hour periods within a 24 hour period and an army of people and then maybe you could get things done.

Q: What do you do for relaxation when you're not working?

SD: I do lots of different sports. I play flag football in a league that I've been playing with for 13 years. We do that all through the winter, so it's fun to get out there in the winter. And during the summer we play in a basketball tournament. I also play softball at the University of Chicago on the weekends. So those take up time, and I have an eight year old, so I hang out with him whenever I can; pretty much that takes up all my time.